Ignition system suitable for internal combustion engines



D. E. STEARNS July 4, 1967 IGNITION SYSTEM SUITABLE FOR INTERNALCOMBUSTION ENGINES Filed Nov. 16, 1964 JYJTEM c R 0mm i m c .Dxck f.Jzeaxws INVENTOR.

ATTOFA/EVJ United States Patent 3,329,867 IGNITION SYSTEM SUITABLE FORINTERNAL COMBUSTION ENGINES Dick E. Stearns, 3103 Ibervilie, Shreveport,La. 71109 Filed Nov. 16, 1964, Ser. No. 411,337 Claims. (Cl. 315-409)This invention relates to an ignition system suitable for internalcombustion engines. It is primarily intended for a system in which anelectronic switch is employed for controlling the discharge of acapacitor through a spark producing apparatus to produce a spark, and inwhich the electronic switch is triggered into conductivity by theapplication of a triggering current thereto upon the opening of thebreaker points employed with such an ignition system. It has for itsgeneral object the inhibition of refiring which may be found to occur insuch a system during breaker point reclosure action as a result ofcontact bounce charactrized by one or more unintended reopenings andreclosures of the breaker points pursuant to the initial breaker pointreclosure after having fired the system. It is also applicable in itsbroadest aspects to other systems in which such premature refiring mayoccur.

In engine ignition systems obtaining spark-over voltage in the sparkplugs by means of the discharge of an energy storing capacitor to theprimary of an ignition transformer and utilizing breaker point openingas a means of initiating the discharge of such energy storing capacitorand hence of the spark formation, operation may be made inefiicient bybreaker point chatter as the points close. This will result in energywasting multiple discharges of the energy storage capacitor.

It is an object of this invention therefore to provide an ignitionsystem, using breaker points of more or less conventional varietyemployed in distributors of internal combustion engines, said systemhaving incorporated therein a means for inhibiting the misfiring of theignition as a consequence of breaker point chatter upon closure ofbreaker points.

It is a further object of this invention to provide an ignition systememploying breaker points of more or less conventional variety such asused in the distributors of internal combustion engines, in which thesystem, having once fired upon opening of the breaker points,instantaneously will assume a condition in which it is unable to causefiring, and will thereafter gradually recover to a condition able tocause firing only after the breaker points shall have closed and allchattering of the points has ceased.

It is a further object of this invention to provide an ignition systememploying breaker points of more or less conventional variety as used inthe distributors of internal combustion engines, in which the system,upon being switched on by a charging current through a firing controlcapacitor upon the opening of the breaker points, will inhibit furtherfiring until said control capacitor is substantially discharged, andwill upon reclosing of said points bleed off the charge from saidcapacitor at a gradual rate such as will reduce it enough to permitfiring only after the breaker points shall have been closed andchattering thereof has ceased.

Other objects and advantages of this invention will become apparent fromthe following description taken in connection with the accompanyingdrawings wherein is set forth by way of illustration and example aspecific embodiment of the invention.

In the drawing:

FIG. 1 is an electrical diagram of an ignition system constructed inaccordance wtih this invention, illustrating in block form the source ofpower providing the energy for the creation of the spark.

FIG. 2 is an electrical diagram illustrating one suitable ice form of asource of power which has been found to operate most satisfactorily forthe purpose of supplying power for sparking to the ignition systemillustrated in FIG. 1, such ignition system being indicated in blockform in FIG. 2.

Referring first to FIG. 1, there is illustrated in electrical diagramform an ignition system utilizing a capacitor discharge of an energystoring capacitor incorporated in a DC to DC power converter, suchdischarge taking place through an ignition transformer as a means offorming a high voltage impulse producing a spark in the sparkplug of anengine to obtain fuel ignition.

With more specific reference to FIG. 1, energy from the battery 1 isconverted to a convenient voltage by a power converter 2 and stored inan energy storing capacitor 31 which is actually a part of the converter2 but is shown in FIG. 1 externally thereof for clarity and conveniencein description. The primary of an ignition transformer or so-calledignition coil 3 is connected to ground through a silicon controlledrectifier 4 which serves as an electronic switch providing for currentflow in one direction from the primary of such transformer to theground. Reverse flow of current from the ground to the primary oftransformer 3 is provided for by means of a diode 5 connectedtherebetween in parallel with the silicon controlled rectifier 4. Theoutput of the ignition transformer secondary is connected in well knownfashion to the various spark plugs in the engine in a system designatedand illustrated diagrammatically at 6. The primary of the transformer 3is connected by a suitable conductor 7 to the positive side of thecapacitor 31 Which serves as the energy storing capacitor for the powerconverter 2 with the opposite side of this capacitor being grounded, itwill be seen that upon the application of a sufiicient signal in theform of a triggering current to the gate of the silicon controlledrectifier 4, the capacitor 31 will be discharged through the primary ofthe transformer 3 and will cause the firing of the spark plug or sparkplugs through the system 6.

In the condition of the system illustrated in FIG. 1, the battery 1provides a unidirectional current source and such source is employed forsupplying a triggering current or signal to the electronic switch 4.Means for conducting a triggering current from the battery 1 to theswitch 4 is provided in the form of a resistance 8, a capacitor 10, anda diode 9 polarized in a direction to permit current flow toward theswitch 4, all three elements connected in series from the positiveterminal of battery 1, to the gate of the switch 4. Shunted across thecapacitor 10 is a high impedance connection or resistor 11. The meansjust described for conducting a triggering current from the battery 1 tothe switch 4 is made up of components of such value as to permit asufficient rate of current flow therethrough for a short period of timeadequate to-trigger or fire the silicon controlled rectifier 4. Resistor11 is of such high impedance as to render it incapable of passingcurrent from battery 1 to the gate of switch 4 of any appreciable degreeunder any condition during the entire firing sequence between one sparkand the next.

Breaker points 12 and 13 are provided interconnected with the battery 1and the gate so that when closed they will short circuit the firingsystem by connecting the juncture between the resistor 8 and thecapacitor 10-, to ground. Thus when these points are closed no currentcan flow and any previous current flow from battery 1 through the RCcombination of condenser 10 and resistor 8 to the I gate of the siliconcontrolled rectifier 4 will be interrupted.

In other words, this closing of the points 12 and 13 connects resistor 8to ground and thus completely cuts off current to the gate of switch 4.

Furthermore, it will be seen that by grounding a point of the circuitbetween resistor 8 and capacitor 10 the closing of the points 12 and 13isolates the RC combination of capacitor 10 and resistor 11 between theaforesaid ground connection at one side of capictor 10 charged to apositive polarity, and the opposite side of capacitor 10 at a negativepolarity blocked below ground potential from any effect on the gate ofswitch 4 by rectifier 9. Under these circumstances the charge oncapacitor 10 will be gradually bled off by resistor 11 toward acondition of zero charge, at least until it reaches a condition ofcharge in which it will be ready to transmit a positive surge ofsufficient current from the battery 1 through resistor 8 and capacitor10 to trigger switch 4 when the breaker points 12 and 13 are next openedto produce a spark.

As is customary in ignition systems for internal combustion engines,there is provided in this instance a cam illustrated diagrammatically at14 for opening the points 12 and 13 when the ignition system is to befired. When the points 12 and 13 are opened by the cam 14, the fullvoltage of the current source 1 will be impressed across the combinedresistor 8, the RC combination control capacitor 10 and resistor 11,diode 9, and the gate-cathode circuit of switch 4, with the result thata surge of current will take place therethrough to the gate of thesilicon controlled rectifier or switch 4. It is to be noted thatinasmuch as with the points 12 and 13 closed the two sides of thecapacitor 10 would eventually reach the same potential due to bleed-offby resistor 11, and hence the capacitor 10 being at least substantiallydischarged at the time the points thereafter opened, its condition ofremanent charge would be such as to enable it to conduct a chargingsurge of current to the gate of the switch 4 sufficient for triggeringthereof.

As previously stated, the application of the surge of current to theswitch 4 will serve to fire the same or render it conductive whereuponthe energy storing capacitor 31 incorporated with the power converter 2will be discharged through the primary of the transformer 3 and theelectronic switch 4 to the ground. This discharge will provide theenergy in the secondary of the transformer 3 to produce the desiredspark which is the object of the system 6.

The anode-cathode circuit of switch 4 having been rendered c nductive bythe gate current as just described, the surge of discharging currentfrom the capacitor 31 through the inductance of the primary of thetransformer 3 will initiate an oscillation beginning with a forwardsurge of current from capacitor 31 and culminating in a reverse surge ofcurrent from the ground back through the primary of the transformer 3 tothe capacitor 31 of the power converter, but since such reverse surgecannot take place through the switch 4 the diode 5 is provided for thispurpose. This leaves the energy storing capacitor 31 with its beginningcharge partly restored and ready to be recharged by the power converterto the desired predetermined degree so as to be ready for producinganother impulse of power to the transformer 3. The action of the reversesurge of current just described will, of course, produce a back biasingof the silicon controlled rectifier 4 as a result of which it willrecover its ability, during the time required for passing through thesaid reverse surge, to block flow of current through its anodecathodecircuit from the energy storing capacitor to the ground until the nextdeliberate firing of switch 4 by the opening of breaker points 12 and 13as hereinbefore described.

After the firing of the system takes place in the manner just described,continued operation of the means for opening the points 12 and 13 willpermit them to close, again establishing the condition in which thejuncture between the resistor 8 and the capacitor 10 is connected toground. When this occurs no further fiow of current from the battery 1to the gate of switch 4 through the capacitor 10 can take place, and thecharge placed on the control capacitor 10 by the previous surge ofgating current, or

triggering current, to the switch 4 will begin to bleed off through theresistor 11. Resistor 11 is selected so that this bleeding action willresult in control capacitor 10 being reduced in charge at least to apoint which differs by at least a predetermined minimum from theultimate charge which the potential of the battery 1 will enable it toplace on the capacitor 10 with the points open, at which point of chargeit will be capable of absorbing sufficient charging current to fireswitch 4, as such charging current simultaneously flows into the gatethereof in series therewith, upon next deliberate opening of the breakerpoints 12 and 13. It will be recognized that immediately after the surgeof current through the control capacitor 10 to the gate of the switch 4,capacitor 10 will have been charged to the full potential of the battery1, and thus will terminate all flow of current from battery 1 to thegate of switch 4 except for the negligible and ineffectual currentpassing through the high impedance of bleeder resistor 11. It will beclear also to those skilled in the art that as the charge on thecapacitor 10 approaches such full battery potential, the currenttherethrough to said gate will be reduced until its rate will be lessthan sufiicient to trigger the switch 4. Thereafter, until reduction ofsaid charge to below said minimum no further firing can occur.

In accordance with this invention the bleeder resistor 11 is made of avalue such that the charge on the capacitor 10 resulting from the firingcurrent to the gate of switch 4 taking place upon the deliberateperiodic opening of breaker points 12 and 13, will not, followingsubsequent periodic initial reclosure of breaker points 12 and 13, bebled down sufiiciently to enable it to again pass a gate current of amagnitude to cause firing of the switch 4 until sufiicient time haspassed to permit all chattering of breaker points 12 and 13, i.e., aseries of spurious rapid reopenings and reclosings, to cease. Thus, eventhough breaker points 12 and 13 bounce open and closed many times aftercoming together initially in their periodic action, the time of suchbounce following the initial closing, as related to the bleed-off rateof capacitor 11} by the resistor 11, is such that upon the occurrence ofany bounce there will still remain sufficient charge on the capacitor 10to prevent the capacitor 10 from passing current at a suflicient rate tofire the switch 4. Thus the switch 4 will not become conductive duringthe bounce period and there will be no false firing. However, theresistor 11 must be chosen to be of such a value that it will bleed offthe charge from the capacitor 10 after the last bounce sufiicientlytopermit refiring, within a time interval less than that before the nextperiodic intentional reopening of the points 12 and 13 during thefastest contemplated operation of the device.

Reference is now had to FIG. 2 in which is illustrated one form of powerconverter which has been found highly satisfactory for the supplying ofpower to the ignition system of this invention as illustrated in FIG. 1.

The source of power for operating the power converter 2 may be the samebattery 1 referred to in FIG. 1, the same having its negative sidegrounded at 20. The positive side of this battery is applied to thecenter tap 21 of the primary of the power transformer 22 having a linearmagnetizing characteristic. The application of the potential of thebattery 1 to the feedback position 23 of the primary winding willproduce a signal current through the capacitor 24 and resistor 25 to thebase of an electronic switch 26 causing the emiter collector circuit ofthis switch to become conductive and connect the lower end of the powerinput winding 27 of the transformer 22 to the ground.

The windings 23 and 27 are arranged in a positive feedback manner sothat when the electronic switch 26 becomes conductive increased basecurrent through the capacitor resistor combination 24, 25 to thetransistor 26 is caused by the resulting transformer response.Similarly, reducing the transistor conductance through the transistor 26causes a resulting decrease in base current through transformerresponse.

The transformer 22 has a secondary winding 28 connected across theterminals of a capacitor 29. The inductance of the winding 28 and thecapacitance of the capacitor 29 provide a tuned oscillatory circuitadapted to operate at a predetermined frequency which establishes afrequency of operation for the converter. One of the terminals of thecoil 28 and capacitor 29 is grounded and the other terminal of thiscombination is connected through a diode 30 to the energy storagecapacitor 31, the opposite side of which is also grounded.

Interconnecting the juncture between the diode 30 and the capacitor -31on one hand and the base of a second electronic switch or transistor 32on the other hand is a conductor '33 having interposed therein a diode'34 and a zener diode 35. It will be appreciated that when the potentialacross the capacitor 31 exceeds the inherent impedance of the zenerdiode circuit and the zener voltage of the zener diode 35, a controlcurrent will flow therethrough to the base of the electronic switch 32rendering its collector emitter circuit conductive. Inasmuch as thiscollector emitter circuit interconnects the base of the electronicswitch 26 and ground, it will be understood that when it becomesconductive it will bleed oft any signal otherwise being passed to thebase of the transistor 26 and make it impossible for such signal torender the transistor 26 conductive. Transistor 26 will then shut olfthe how of current through the power input coil 27 and stop the feedingof power through the transformer 22 to the energy storing capacitor 31.

Diode 34 will prevent any negative surge of potential by the energystoring capacitor 31 from causing destructive reverse flow of currentthrough the zener diode 35.

The converter circuit having been shut down by the charge on capacitor31 exceeding a predetermined voltage and causing a shut-down signal toflow through the zener diode 35 as above described, when the voltage onthe capacitor 31 again falls sufiiciently to permit the zener diode tohold the output voltage and stop passing control current, the transistor32 will become nonconductive, the signal from winding 23 will againbecome effective to render the collector emitter circuit of thetransistor 26 conductive, and the converter will resume oscillation andcharging of the energy storage capacitor 31 back to the level at which asignal will be passed through the zener diode -35 to shut it off again.

From the foregoing it will be seen that this invention is one welladapted to attain all of the ends and objects hereinabove set forth,together with other advantages which are obvious and which are inherentto the apparatus.

It will be understood that certain features and subcombinations are ofutility and may be employed Without reference to other features andsubcombinations. This is contemplated by and is within the scope of theclaims.

As many possible embodiments may be made of the invention withoutdeparting from the scope thereof, it is to be understood that all matterherein set forth or shown in the accompanying drawings is to beinterpreted as illustrative and not in a limiting sense.

The invention having been described what is claimed is:

1. In an ignition system of the type having an energy storing capacitor,an ignition coil and an electronic switch interconnected therewith forconnecting said capacitor to said coil to discharge therethrough andprovide a spark when said switch is rendered conductive, said switchhaving a control gate and being of the type rendered conductive uponsupply of a current to said gate at a triggering rate, and meansincluding a unidirectional current source and breaker pointsinterconnected with said current source and gate for alternatelysupplying and interrupting current flow to said gate upon make and breakoperation of said points, and in which said points in high speedoperation tend to bounce open during a time interval after closing andthereby cause unwanted firing; the improvement which comprises: anelectrical energy storing means connected between said current sourceand said gate to undergo a change in its electrical charge in onedirection upon flow of current through the storing means to said gate ina triggering direction and to cause reduction in rate of such flow assaid change in charge progresses until it reduces such flow to less thana triggering rate when its charge approaches within a predeterminedminimum of the ultimate charge it could attain due to such flow, wherebywhile its charge is within said minimum of said ultimate chargeadditional firing is inhibited, and the circuit through said energystoring mean-s and said gate has a relatively low transient impedance,isolating means connected in series with said energy storing means andsaid gate responsive to breaker point action in said interrupting ofcurrent flow to said gate, and relatively high impedance means connectedto said storing means for conducting reverse flow through said storingmeans at a rate to delay its return to a state of charge outside saidminimum for a greater time than required for the termination of bouncingtendency of the breaker points after closing.

2. The improvement in an ignition system as set forth in claim 1 inwhich said isolating means includes a rectifier in series in the gatecircuit to prevent the reverse flow from following the low impedancepath through said gate.

3. The improvement in an ignition system as set forth in claim 1 inwhich said electrical energy storing means is a capacitor and in whichthe operation of said breaker points serves alternately to impressacross said capacitor the voltage of said current source and toeffectively remove the voltage of said current source from saidcapacitor to alternately charge and discharge said capacitor and inwhich current flowing through said capacitor to said gate causing changeof the charge on said capacitor in one direction is provided with a lowimpedance path whereby such change may take place relatively rapidly,and the relatively high impedance means is the only path available forsuch reverse flow through said capacitor.

4. The improvement in an ignition system as set forth in claim 1 inwhich said electrical energy storing means is a capacitor and saidisolating means is a rectifier in series between said current source andsaid gate to permit current flow therethrough in a triggering directiononly, said high impedance means includes a resistor shunted across saidcapacitor of a resistance snflicient to prevent a reduction of thecharge on said capacitor from the full charge which said current sourceis capable of impressing thereon to below said predetermined minimum fora greater time than required for the termination of bouncing tendency ofthe breaker points after closing, and in which there is a resistor inseries with said breaker points across said current source.

5. A power supply and control circuit combination for use in an ignitionsystem of the type wherein a spark is produced by discharging electricalenergy through an ignition coil in consequence of the operation of abreaker point type switch between its open and closed positions and inwhich the breaker points of such switch in high speed operation tend tobounce open upon closing and thus cause unwanted firing, said powersupply and control circuit component combination comprising: a powersupply including an energy storing capacitor and means connected theretofor recharging said capacitor upon reduction of its charge below apredetermined condition of charge; an ignition coil; an electronicswitch of the type having a control gate and rendered conductive by atriggering current to said control gate, said coil and switch beingconnected to said energy storing capacitor to receive a discharge ofcurrent from said capacitor through said coil and thereby produce aspark when said switch is rendered conductive; current conducting meansconnected to said control gate of said switch and adapted to beconnected to a current source for producing triggering current to thecontrol gate of said switch, said conducting means including: a secondelectrical energy storing means connected between said current sourceand said gate to undergo a change in its electrical charge in onedirection upon flow of current through the storing means to said gate ina triggering direction and to cause reduction in the rate of such flowas said change in charge progresses until it reduces such flow to lessthan a triggering rate when its charge approaches within a predeterminedminimum of the ultimate charge it could attain due to such flow, wherebywhile its charge is within said minimum of said ultimate chargeadditional firing is inhibited and the circuit through said secondenergy storing means and said gate has a relatively low transientimpedance, isolating means connected in series with said second energystoring means and said responsive to said breaker point action in saidinterrupting of current flow to said gate and relatively high impedancemeans connected to said second storing means for conducting reverse flowthrough said second storing means at a rate to delay its return to astate of charge outside said minimum for a greater time than requiredfor the termination of bouncing tendency of the breaker points afterclosing.

' References Cited UNITED STATES PATENTS 2,888,574 5/1959 Buon 3152093,078,391 2/ 1963 Bunodiere 315-209 3,165,688 1/1965 Gutzwiller 315-100JOHN W. HUCKERT, Primary Examiner.

D. O. KMFT, Assistant Examiner.

1. IN AN IGNITION SYSTEM OF THE TYPE HAVING AN ENERGY STORING CAPACITOR,AN IGNITION COIL AND AN ELECTRONIC SWITCH INTERCONNECTED THEREWITH FORCONNECTING SAID CAPACITOR TO SAID COIL TO DISCHARGE THERETHROUGH ANDPROVIDE A SPARK WHEN SAID SWITCH IS RENDERED CONDUCTIVE, SAID SWITCHHAVING A CONTROL GATE AND BEING OF THE TYPE RENDERED CONDUCTIVE UPONSUPPLY OF A CURRENT TO SAID GATE AT A TRIGGERING RATE, AND MEANSINCLUDING A UNIDIRECTIONAL CURRENT SOURCE AND BREAKER POINTSINTERCONNECTED WITH SAID CURRENT SOURCE AND GATE FOR ALTERNATELYSUPPLYING AND INTERRUPTING CURRENT FLOW TO SAID GATE UPON MAKE AND BRAKEOPERATION OF SAID POINTS, AND IN WHICH SAID POINTS IN HIGH SPEEDOPERATION TEND TO BOUNCE OPEN DURING A TIME INTERVAL AFTER CLOSING ANDTHEREBY CAUSE UNWANTED FIRING; THE IMPROVEMENT WHICH COMPRISES: ANELECTRICAL ENERGY STORING MEANS CONNECTED BETWEEN SAID CURRENT SOURCEAND SAID GATE TO UNDERGO A CHANGE IN ITS ELECTRICAL CHARGE IN ONEDIRECTION UPON FLOW OF CURRENT THROUGH THE STORING MEANS TO SAID GATE INA TRIGGERING DIRECTION AND TO CAUSE REDUCTION IN RATE OF SUCH FLOW ASSAID CHANGE IN CHARGE PROGRESSES UNTIL IT REDUCES SUCH FLOW TO LESS THANA TRIGGERING RATE WHEN ITS CHARGE APPROACHES WITHIN A PREDETERMINEDMINIMUM OF THE ULTIMATE CHARGE IT COULD ATTAIN DUE TO SUCH FLOW, WHEREBYWHILE ITS CHARGE IS WITHIN SAID MINIMUM OF SAID ULTIMATE CHARGEADDITIONAL FIRING IS INHIBITED, AND THE CIRCUIT THROUGH SAID ENERGYSTORING MEANS AND SAID GATE HAS A RELATIVELY LOW TRANSIENT IMPEDANCE,ISOLATING MEANS CONNECTED IN SERIES WITH SAID ENERGY STORING MEANS ANDSAID GATE RESPONSIVE TO BREAKER POINT ACTION IN SAID INTERRUPTING OFCURRENT FLOW TO SAID GATE, AND RELATIVELY HIGH IMPEDANCE MEANS CONNECTEDTO SAID STORING MEANS FOR CONDUCTING REVERSE FLOW THROUGH SAID STORINGMEANS FOR CONDUCTING ITS RETURN TO A STATE OF CHARGE OUTSIDE SAIDMINIMUM FOR A GREATER TIME THAN REQUIRED FOR THE TERMINATION OF BOUNCINGTENDENCY OF THE BREAKER POINTS AFTER CLOSING.